(1) Field of the Invention
This invention relates to a pattern position detecting system, and more particularly to a pattern position detecting system which automatically and speedily detects the position of a specified pattern existent on the surface of an object body by utilizing an imaging device.
(2) Description of the Prior Art
Systems wherein a certain target pattern is sampled from among images picked up by an imaging device such as television camera, in a manner to be distinguished from other patterns and a background pattern and has its position within a two-dimensional image obtained, have been already proposed in Japanese Patent Application Publication No. 52-14112 (U.S. Pat. No. 3,898,617) and Japanese Published Unexamined Patent Application No. 52-91331. These systems find the specified position of an object in such a way that a local pattern of an object surface is stored as a standard pattern in advance, that the standard pattern and partial patterns cut out in various positions within the image as fed by the imaging device are successively compared, and that positional coordinates typical of the partial pattern which best coincide are sampled. These systems are applied to, for example, the position detection of a semiconductor pellet when the wire bonding between bonding pads formed on the semiconductor pellet and lead fingers is automatically carried out.
In the prior-art systems, however, the target pattern is identified by finding the position of the pattern best coincident with the standard pattern within the image, so that only a pattern having an inherent feature which is not included in the other patterns on the object can become the target pattern. Accordingly, in case where a pattern having such an inherent feature does not exist on the object or where the pattern having the inherent feature exists only in a position which is inconvenient for grasping the positional deviation or rotational deviation of the object, the prior-art systems cannot achieve the expected purpose and their ranges of applications have been limited.
For example, when a part of a digitated electrode of a high power transistor having cyclic patterns or one of a plurality of electrodes or bonding pads in the same shape as formed in the edges of a chip of an IC (integrated circuit) or an LSI (large scale integration) is intended to have its position detected as the target pattern, the electrode part to be made the detection target needs to be put into a special shape at the stage of the design of the electrode pattern in order to apply either of the prior-art systems.